Managing a storage area of a storage device for a computer by a file system requires a mapping/interpreting function supporting the file system, and this function has to be mounted on a software or a hardware.
The mount of the mapping function on the hardware increases cost and complicates the hardware. Therefore, the mapping/interpreting function is mounted on the software in general. Some widely-spread operating systems (OS) provides mapping/interpreting function supporting some file systems in advance.
In the case of employing a file system not supported by an OS (hereinafter called a unique file system), there are two methods for providing the mapping/interpreting function as follows.
The first method is locating a unique file system entity directly on a physical storage area and interpreting the file system by a kernel mode software (in general, a file system driver) which supports the unique file system and has the same interface as interpretation software for the OS. Hereinafter, this accessing method is called as a kernel mode access.
In this case, a user can access a file disposed on the unique file system by the user interface (UI) for the OS.
However, according to this method, it is necessary to install the kernel mode software on the OS. Thus, under the log-in environment where the installation of the kernel mode software is inhibited according to the security policy, it is necessary to install the kernel mode software after switching an administrator mode into the log-in circumstance allowing the installation of the kernel mode software. This will be a large load for a company where an administrator manages personal computers for several tens or several hundreds persons.
The second method is locating the unique file system entity within a file system entity supported by the OS (herein after called a standard file system). Hereinafter, this system is called a double file system structure. In this case, since the unique file system entity is recognized as a single or a plurality of file images defined by the standard file system, it is possible to access the unique file system entity when a unique user mode application having a function of interpreting the unique file system accesses the single or the plurality of file images (hereinafter called a user mode access).
According to the second method, the unique file system is accessible without installing the kernel mode software, and there is no problem of the first method even under the login environment with a strict security policy. However, according to this method, since the file is operated by a unique UI of the unique application, a user must operate the file with the operability different from the UI of the OS.
JP-T-2006-523882 discloses a method for mutually relating a first file system and a second file system.
If a single unique file system can be accessed by the above two methods, improved utility can be provided. For example, it is possible to provide a utilizing method as follows: for a personal computer which frequently uses the unique file system, the kernel access mode is employed to improve the utility; and for a personal computer which temporarily uses the unique file system, the user access mode is employed to improve the operability.
Although the double file system structure allows this utilization method, there may arise two problems.
The first problem is that since the OS analyzes the double file system structure, the performance is degraded and the utilizing ratio of a CPU increases as compared with mapping a single file system structure.
Since the kernel access mode is intended to a frequent use, it is desirable to prevent the degradation of the performance and the increase of the utilizing ratio of the CPU, which is a first object.
The second problem is that in the case of recognizing the unique file system entity as a file image, there arises a risk that the unique file system entity may be deleted or modified by a procedure of deleting or modifying a single file system.
Since a plurality of files (several thousand or several ten thousand files in some case) may be deleted simultaneously in response to an operation of deleting a single file by a user, such the risk caused by an erroneous operation of a user is high, and a second object is to prevent this problem.
JP-T-2006-523882 discloses a system in which a recording medium employing the first file system is accessed via an interface employing the second file system. Such the double file system structure can not be employed.